1. Field of the Invention
This invention relates to a means for joining or seaming structurally composite cellulose containing materials, and is particularly applicable to structurally composite, fibrous containing cellulosic materials which have been regenerated from viscose. The invention has broad application to multiple structural forms of cellulose containing material including tubes, sheets, pieces, and webs but has primary utility in the formation of artificial sausage casing.
2. Prior Art
The manufacture of artificial tubular casings from regenerated cellulose has been practiced for many years, particularly for use in the processing of frankfurters and related sausage products such as bologna, ham, and the like. The process essentially comprises extruding regenerated cellulose in a tube in the form of non-fibrous reinforced or forming a fibrous web of material into a tube and extruding viscose about the exterior and interior of the tube formed web; coagulating and regenerating the viscose to form a cellulosic tube; washing, plasticizing, and drying to form the completed tube. Though the process is well known and widely practiced, the equipment is complex and the problems associated with the process are numerous. A particular problem is the formation of gaseous byproducts during the viscose regeneration step which require means for venting the formed tube and may even require the purposeful cutting of the formed tube to prevent damage from the entrapped gases. Another problem is the formation of a composite structure by treatment of the completed tube with various functional coatings, on either or both of the exterior or interior of the tube, that may be required in the final product. By composite structure is meant cellulosic material containing one or more functional coatings on either or both sides. By functional coating is meant a coating, continuous or discontinuous at the interior and/or exterior surface of the tubing, of a composition which acts to modify the mechanical, biological and/or chemical characteristics of the cellulosic tubing surface.
The application of functional coatings to form structurally composite materials has always presented a problem in the conventional method of forming cellulose tubing, particularly coatings contained on the interior of the tube. Typically, an interior coating is applied by breaching the integrity of a coagulated and regenerated tube and inserting into the breached tube a "slug" of liquid coating material. If the slug is maintained at a low point, through which the tube is continuously processed, the liquid slug will continuously contact the interior wall thereof. Use of a slug, however, has many problems in that it is difficult to control the amount and consistency of functional coatings being applied and requires cutting the tube and interrupting the continuous manufacture of the tubing for replenishing the slug or correcting other multiple problems that might occur. In such method, the manufacturer is at the mercy of the physical characteristics of the liquid slug itself and has very limited means to mechanically control the thickness, amount, continuity, or even consistency of the applied coating. Another method of coating the interior of tubing is to treat the exterior of the completed tubing and evert the tubing to gain placement of the exterior coating on the interior surface. Everting processes provide an advantage in that the amount and thickness of the coating can be mechanically controlled, but the delicacy of coating the exterior of an inflated tube and the stress problems associated with turning inside out a coated tube represent significant barriers to commercial acceptability. Such process also requires complex machinery and cannot be performed on a continuous tube. Thus, the application of functional coatings, particularly interior coatings, in the conventional manufacture of cellulosic tubing has fostered a complex and costly industry in and of itself.
In order to avoid at least some of the cost and complexities of the existing conventional method of forming composite cellulose tubing, it has been thought to be desirable to manufacture flat webs of cellulose material to their completed form, which can be provided with functional coatings or otherwise treated, and, thereafter form the desired tubing by longitudinally seaming the web. Though the longitudinal seaming of webs of cellulose containing material has been the subject of many patents and other publications, no seaming means has heretofore been found which prepares a seam good enough to enjoy wide commercial use in the manufacture of regenerated cellulose sausage casings. Inevitably, each of the prior art attempts at seaming a tubular casing has resulted in a variety of problems, such as the weakening of the casing at the seam or points adjacent to the seam, weakening of the seam by application of functional coatings, web distortion caused by the seaming process, duplication of processing steps, or other problems associated with the formation or presence of a seam.
Typically, in prior art means of seaming cellulose webs, the presence of a functional coating at the point of seaming adds to the seaming problem, causing further difficult to detect seam strength and adherence defects. Invariably, subjecting the resulting tube to smoke house conditions, stuffing, soaking or rewetting the casing in accord with common commercial practice, results in exaggerated weaknesses at the casing seam or adjacent points which in turn causes failures or distortions of the stuffed casing. Thus, a real need exists for an inexpensive and speedy process for the seaming of flexible casing material.
U.S. Pat. No. 2,952,550 proposes a method of seaming fibrous reinforced cellulose structures by the application of various specific adhesives to overlapped edges of a sheet or web, which does not contain a functional coating but otherwise is a completely processed, regenerated cellulose fibrous material. Amongst the multiple adhesives disclosed in the patent, Example XI describes the formation of the completed tube by sealing uncoated commercial fibrous casing lengthwise, utilizing a thermoplastic material sealing apparatus, by applying a 75% aqueous solution of zinc chloride between the overlapped edges of the casing, pressing together the overlapped seam and substantially immediately washing the seamed tube by passing it through a water bath to wash out the zinc chloride. The washing step is described as a critical step in the process, necessary to remove the highly acidic zinc chloride solution which otherwise is seen to act quickly on the uncoated cellulosic material of the example to degrade and weaken it. The thus washed, seamed, fibrous reinforced tubing then requires further plasticizing and drying in accord with the process of forming regenerated cellulose to provide an adequate completed product.
Such sealing process, as described in U.S. Pat. No. 2,952,550, is very costly because of the necessary repetition of washing, plasticizing, and drying steps. It does not solve the problem of applying a functional coating and cannot be used on unreinforced cellulosic material. The thermoplastic sealing apparatus utilized in the patent heats the seal to such high temperature (&gt;150.degree. C.), to cause fusion in accord with thermoplastic material processing as recommended by U.S. Pat. No. 2,330,446, that even fibrous reinforced cellulose webs become weakened and burst in areas adjacent to the seam. Further, the required substantially immediate imposition of a washing step removing the zinc chloride before the seam is cured, adversely affects the dried casing by significantly reducing its stretchability and necessitates additional plasticizing and drying steps, which significantly increases the cost inherent therewith. Even with the incorporation of these additional steps, the resulting completed tubing product displays uneven characteristic at the seam in comparison to the remainder of the casing. Such process, as proposed in U.S. Pat. No. 2,952,550, is obviously seriously inadequate for commercial utility and as far as it is known has never been commercially implemented.